What's eating my black walnut 'thomas'?

Black walnut 'Thomas' is affected by the same pest complex as all Juglans nigra. Walnut caterpillar is the most destructive foliage feeder, sometimes stripping whole trees. Walnut husk maggot ruins the nut crop. Black walnut curculio is the main nut-boring beetle. Codling moth larvae also consume kernels.

Dark, hairy caterpillars gregarious-feed in July–August, stripping entire branches; a bad outbreak can defoliate the whole tree. Prune and destroy clusters of eggs or young caterpillars before they disperse. Apply Bacillus thuringiensis (Bt) to young larvae. Permit the caterpillars to descend the trunk (they do so to moult) and destroy them at that stage.

Maggots tunnel in the husk causing black, slimy decay; kernels are stained dark and reduced in weight and quality. Monitor adult emergence from late summer. Apply spinosad-based sprays at first adult activity. Remove and destroy fallen, infested nuts immediately.

Female weevil bores into developing nuts and deposits eggs; larvae feed inside the nut, causing early drop with small exit holes. Collect and destroy all dropped nuts promptly to break the larval–soil pupation cycle. Permitted insecticide applied at nut set can reduce adult populations.

Larvae bore into the nut and consume the kernel, with frass-filled entry tunnels visible on the husk. Pheromone traps monitor adult flight. Apply codling moth granulosis virus or spinosad timed to egg hatch. Mating disruption is practical for larger plantings.